The prior art of U.S. Pat. Nos. 4,049,399; 4,337,2239 and 4,401,444 each use the nucleation of submicron contaminant particles from water vapor and the subsequent collection of these nucleated droplets as a means of cleaning flue gas. These prior art processes are restricted to (1) a turbulent isoenthalphic means of nucleation and (2) an isothermal venturi process which causes nucleation. Each of these methods apply specifically to submicron particles and embody a transitory phase where the probability of revaporization of the nuclei prior to separation from the flue gas is very high.
The obvious shortcomings of these processes are: (1) Much of the nucleation which may occur reverses into evaporation before the contaminant droplets can be collected. (2) Neither method specifically defines a means of promoting the accretion of these droplets into the larger drops required for an effective collection process. (3) Neither process effectively operates on particles of greater than 1 micron in size. (4) Neither process attains separation efficiencies approaching current best available control technology.
This invention specifically addresses these shortcomings where an extended state of supersaturation is attained, allowing for complete nucleation on all contaminant particles and for the accretion into the larger droplets required for inertial collection.
A paper presented by C.C Shale in Aug. 29-30, 1972 at the 164th Meeting of the American Chemical Society, titled: Ammonia Injection: A Route to Clean Stacks, describes nucleation as, "The apparent cause for such effective removal of the finely divided salt particles (d.sub.p =0.01 to 1.0 .mu.m) and the residual ash particles . . ." The paper did not describe specific apparatus or methods which cause nucleation, but does state (Table II) that 100% removal of SO.sub.z did occur. This represents the most outstanding example of the references cited that the process of nucleation, if applied correctly, is a truly effective means of flue gas cleanup.